Although woven carpets have been articles of commerce for many years the use of carpets as floor coverings was limited by the relatively high cost of the slow weaving processes employed. With the development of the much more economical and speedy tufting process the potential markets for carpets and rugs in both residential and contract applications have increased dramatically. In this tufting process synthetic or natural fiber yarns are inserted in the form of tufts into a primary backing by a plurality of needles to form a face pile, as is well known in the art. Until these inserted tufts are attached firmly to the primary backing fabric by some form of an adhesive they are readily removed and a tufted carpet without the adhesive has little value. After applying the adhesive the tufts are locked permanently in place. Frequently a compounded synthetic rubber latex is used as an adhesive but other adhesive systems have been developed including the use of hot melt adhesives and tuft locking is no longer a limiting factor in the marketability and use of tufted carpets.
The simple tufting process has been developed over the years and a wide range of tufted carpet styles are now available for many diverse applications in homes, offices and public buildings. As originally developed the primary backing fabrics were primarily cotton but these were rapidly replaced by jute fabrics. With the continued development of the tufting process these jute primary backing fabrics have been largely replaced by woven polypropylene ribbon or tape fabrics or in some styles by spun bonded polypropylene fabrics. These polypropylene ribbons or tapes are produced either by direct extrusion or in many cases by appropriate slitting of extruded polypropylene film.
Since carpets must be both functional and esthetic the characteristics of the face yarns inserted into the fabric, the ability to apply desired color to such yarns and tufted carpets and the tufting design are very important in determining marketability of the final carpets. Primary carpet backing properties are important in determining tufting performance and hence are related to the carpet design. Thus, the selection of the proper primary backing fabric is important in preventing needle deflection and is particularly important in many types of printed carpets. Although polypropylene fabrics have captured a major share of the primary backing market, jute fabrics are still used primarily in shag carpets and in certain types of molded automotive carpets.
In addition to esthetics many of the physical properties of the tufted carpets are related to the amount and type of face yarn employed and the selection of the primary carpet backing as well as the amount and type of adhesive which is applied. However, in order to enhance dimensional stability and resistance to stresses produced by heavy traffic patterns and other factors, it has been common practice to improve these properties of tufted carpets by using a reinforcement fabric of some type. Frequently the reinforcement is provided by laminating a rather open woven fabric to the underside of the tufted carpet. These reinforcing fabrics or secondary carpet backing fabrics provide the additional reinforcement required for satisfactory performance in many tufted carpet applications. Woven jute fabrics weighing from six to eight or more ounces per square yard have been in common use for many years as secondary carpet backing fabrics and have captured a major share of this reinforcement fabric market.
The process of spinning jute yarns from the non-uniform jute fiber is complex and generally results in a yarn which is relatively open and has many protruding fiber ends. As a result the compounded rubber latex used as a laminating adhesive can readily penetrate both the open reinforcing fabric and the jute yarn. Excellent laminate strength is readily obtained and this is one of the distinct advantages of jute secondary carpet backing fabrics. Unfortunately, jute fabrics have certain deficiencies which, combined with their manufacture in foreign countries with long supply lines, have encouraged the development of improved secondary carpet backing fabrics from synthetic fibers or yarns.
Since jute yarns are based on a natural cellulose product derived from the jute plant by an improved process they are subject to all of the variabilities of natural products and, in addition, they are moisture sensitive and are not inherently mildew resistant. In addition, since jute fiber is grown, spun into yarn and woven into fabric in distant foreign countries, the supply of the fabric is subject to many vagaries which are not always under good control. These factors include the effects of disastrous weather on crop productivity, governmental instability and labor unrest in both the fabric production and transportation areas. The result has been a fluctuating supply situation with rapid and uncertain price changes. As a result the development of a satisfactory secondary carpet backing from domestically produced man-made or synthetic materials which would be under much closer domestic control and which would not have the inherent disadvantages of jute has long occupied the attention of many inventors.
Synthetic fibers with their outstanding uniformity, high strength, lowered moisture sensitivity, dimensional stability and inherent mildew resistance, offer an attractive combination of properties. Polyolefin fibers offer an unusual combination of ready availability, high strength, low moisture sensitivity, mildew resistance and low density. The polyolefins, and particularly polypropylene fibers, are based on either by-products or co-products of the huge petroleum refining or petrochemical industries and as a result have a unique supply situation in the United States. Other synthetic fibers are also based on the hugh petrochemical industry and as a result these petrochemical based synthetic fibers offer an ideal base for the development of a secondary carpet backing.
Although the desirability of developing an all synthetic secondary carpet backing fabric has long been recognized, the solution to this problem has been difficult to achieve because of the many technical and economic requirements which must be met. Schwartz, U.S. Pat. No. 3,309,259, was able to demonstrate that some improvement in dimensional stability could be obtained if only a portion of the secondary carpet backing was made from synthetic materials. In these woven fabrics the warp yarns were either made from polyamides or polypropylene yarns whereas the weft yarns were made from a paper yarn, Kraftcord, or jute.
With the development of woven primary carpet backing from polypropylene ribbon or tape yarns with their very favorable economics, it was natural to consider these fabrics for secondary carpet backings. These synthetic fabrics have high strength, good flexibility and dimensional stability, excellent resistance to moisture and good mildew resistance and can be economically produced from polymers derived either as by-products or co-products of the petroleum refining or petrochemical industries and, therefore, in an excellent supply situation. However, despite these favorable characteristics, attempts to use these ribbon fabrics as secondary carpet backing fabrics failed because of poor adhesion of the wide, relatively smooth yarns in the fabric to the tufted carpet. Although satisfactory adhesion to polypropylene primary carpet backing can be developed for tuft locking by using a carboxylated styrene-butadiene rubber latex, the laminate strength of ribbon fabrics, even using ehse improved latices, is not satisfactory and delamination is a serious problem.
Eickhoff, U.S. Pat. No. 3,542,632, recognizing that ribbon or tape polyolefin fabrics had very poor adhesion to tufted carpets, attempted to solve this problem by subjecting the woven ribbon yarn fabric to mechanical treatments which would fibrillate the yarns in the fabric. The fibrillating methods included sand blasting, mechanical abrasion and needle punching with barbed needles as the preferred method. Fabric design, yarn dimensions, and the amount of needling are reportedly critical in determining the suitability of the fabric for secondary backing. Since it is very difficult to control yarn fibrillation by mechanical action on the woven fabric, the resulting fibrils are usually quite coarse and adhesion, although improved, does not reach satisfactory levels without serious impairment to fabric properties. If the finer fibrils required for good adhesion are to be produced the amount of fabric damage resulting from the much higher needle density is extensive and fabric strength is greatly reduced.
Some of the disadvantages of fibrillating a woven fabric can be overcome by fibrillating a yarn and thereafter weaving a fabric using a fibrillated yarn in at least one fabric direction. Although these fabrics have somewhat improved laminate strength, delamination remains a major problem. It is known that hot melt adhesives give improved laminate strength and tuft binding and fabrics woven from fibrillated yarns have found a limited market as secondary carpet backings in those market areas where hot melt adhesives are used.
Fabrics woven from fibrillated yarns in at least one direction have been subjected to mechanical action to preferentially raise fibers on one side of the fabric as taught by Malik, U.S. Pat. No. 4,145,467. Unlike fabrics woven from spun yarns where mechanical action on these fabrics not only breaks fibers but also physically pulls fibers from the yarn bundle, mechanical action on fibrillated yarns can only be effective by breaking the fiber or network structure. As a result, mechanical action, such as by needle punching with barbed needles or by some other mechanical action as abrasive action, results in somewhat improved laminate strength but greatly decreased fabric strength. Thus, some comprimise between laminate and fabric strength must be reached. These fabrics when subjected to carefully controlled mechanical actions and used under controlled conditions have found limited applications.
Since woven jute fabrics have satisfactory adhesion properties to tufted carpets, one of the approaches to producing an all synthetic secondary backing fabric is the use of a spun synthetic yarn. Such yarns can be used in both directions as in the common jute fabrics but for economical reasons attempts have been made to reduce costs by using spun yarns only in the fill direction. Again, for economic reasons, such spun yarns utilize either polyester or preferably polypropylene staple fiber. Since jute yarns are usually quite open and have many loose ends, these characteristics permit latex to penetrate the yarn bundle and improve adhesion. For this reason attempts have been made to develop similar characteristics in the synthetic spun yarns. Again, a compromise between yarn twist and strength must be reached.
One of the characteristics of jute fabrics is its open structure which permits latex to penetrate both the fabric and the yarn bundle as well. Although jute secondary backing fabrics have an open structure the fabrics are reasonably stable, in spite of this open structure, because of the high fiber friction at the yarn crossovers. If similar fabrics are woven using polypropylene ribbon yarns in both directions the friction developed on the smooth ribbon yarns crossovers is quite low and the yarns can be readily displaced. The replacement of the ribbon yarn in the weft direction by a spun polypropylene yarn improves fabric stability slightly but the open fabric is far from satisfactory and the fabrics are readily distorted.
For a number of years open packaging fabrics useful for packaging fruits and vegetables have been woven from polypropylene ribbon yarns using a leno fabric construction. These fabrics have greatly improved stability. Combining the improved adhesion of the synthetic spun yarns with the fabric stability arising from the leno weave pattern, the all synthetic secondary carpet backings which have found the widest acceptance by the trade have used a leno weave pattern with polypropylene ribbon yarns in the warp direction and a spun synthetic yarn, usually of polypropylene, in the weft direction.
Although ribbon-spun yarn secondary carpet backing fabrics produced from synthetic fibers and synthetic spun yarns can have generally satisfactory adhesion properties, the adhesion of these fabrics can be further improved by subjecting the as-woven fabric to mechanical action such as brushing or sanding or the like. Generally such mechanical action is confined to one side of the fabric only but for special purposes both sides of the fabric may be so treated.
Since jute fabrics have been so widely used as secondary carpet backings, process equipment and technology for lamination have been developed over the years for use with these jute fabrics. The acceptance of an all synthetic secondary carpet backing fabric would be greatly enhanced if the same processing equipment used for jute, or at least the same equipment with minor alterations, could be satisfactorily used. As noted, adhesion is related not only to the fabric composition, design and fabrication, but it is also related to the adhesive employed and by the method of application of the adhesive. Since compounded synthetic rubber latices are so widely used by the tufted carpet industry for tuft locking and are so economical, it is preferred that any improved synthetic secondary carpet backing be useful with this adhesive system. Since the strength of the adhesive bond is related in part to the type and amount of latex used, the composition of the latex compound and the method of application and curing of the latex compound, these factors must be considered in the selection and utilization of a secondary carpet backing fabric. Thus, the total cost-performance of the all synthetic fiber secondary carpet backing fabric system becomes a major factor in the acceptability of the fabric by industry.
Although the ribbon-spun yarn leno woven secondary carpet backing fabrics have many desirable properties, the adhesion of the as-woven backing to the tufted carpet is related not only to the fabric design, construction and fabrication, but also to the properties of the spun yarn. Yarn properties are related in turn to stable fiber properties and to the yarn spinning process which is employed. As staple lengths and twist levels are increased to improve yarn strength the number of fiber ends and the ability of the latex to penetrate the yarn bundle is reduced. As a result the laminate bond strength is generally reduced as yarn twist is increased.
Spun yarn costs represent one of the major costs in the production of ribbon-spun yarn leno secondary carpet backing fabrics. These spun yarn costs include not only the costs of converting monomers or polymers into staple fibers but also the very substantial costs of converting staple into spun yarn. These latter charges include not only the very substantial capital charge costs but also the rather high labor costs involved in conventional spinning processes. These costs are so high that major efforts to reduce the costs of converting staple into yarn are under continuous investigation. Although yarn costs have been reduced by the development of open end rotor spinning or by the modified Dreft system, spun yarn costs remain a substantial part of the cost of producing synthetic secondary carpet backing. Furthermore, the large capital investment required for an efficiently sized plant represents a major deterrent to many potential producers of secondary carpet backing.
There have been other proposals for producing secondary carpet backing fabrics which involve either the use of non-woven structure or some modification of this non-woven structure. In several cases the non-woven structures were produced by needle punching processes. Generally those fabrics which are produced soley by needle punching processes have little fabric strength at low fabric weights and fabrics with adequate strength for good reinforcement require so much fiber that fabric costs are excessive. Again, attempts have been made to use woven ribbon fabrics onto which a light coating of fiber have been needled. Generally such fabrics have a rather tightly woven structure which prevents latex from penetrating the needled fabric and since the fabrics are only lightly needled the fibers can be readily pulled out and laminate strengths are low.
Although many processes have been proposed for producing secondary carpet backings major compromises must be reached between the physical properties of the fabric as a reinforcing fabric, the strength of the laminate to the tufted carpet, and the economics of production of the fabric. As a result the development of improved secondary carpet backing fabrics from synthetic fibers remains an active development field. Thus, one of the objectives of this invention is the development of secondary backing fabrics which have controlled but variable levels of adhesion without impairment of fabric physical properties as a reinforcing agent for tufted carpets. Another objective of this invention is the development of secondary carpet backing fabrics with controllable but variable adhesion in the as-woven condition requiring no additional mechanical action as the as-woven fabric. Another objective of this invention is the production of as-woven secondary carpet backing fabrics with controlled high levels of adhesion on both fabric sides without resorting to mechanical action on the as-woven fabric. Another important objective of this invention is the reduction in capital requirements for converting synthetic fibers into yarns and fabrics suitable as secondary carpet backing fabrics. Yet another objective of this invention is the more economical use of synthetic fibers in the development of satisfactory secondary carpet backing fabrics. Other objectives of this invention will be apparent from the description of the invention to those skilled in the art.